Patent documents 1 to 3, for example, describe fabrication methods of conventional semiconductor devices.
Patent document 1 describes a method to round an angular corner of the bottom of a trench by isotropic etching after formation of the trench on a silicon substrate by anisotropic etching. According to this method a RIE (Reactive Ion Etching) device is used for the anisotropic etching and a CDE (Chemical Dry Etching) device is used for the isotropic etching. A mixture gas of SF6 or CF4 and O2 gases is used as an etching gas for the isotropic etching.
Patent document 2 describes a method of lateral etching at the bottom of a trench by isotropic etching after formation of the trench on a silicon substrate by anisotropic etching. According to this method a mixture gas including Cl2 and O2 gases is used as an etching gas for the isotropic etching.
Patent document 3 describes a method of formation of a trench by dry etching of a silicon substrate using a mixture gas of CF4 and Cl2 gases as an etching gas under application of a bias voltage.
[Patent Document 1]
Japanese Patent Kokai Publication No. JP-P2001-244325A
[Patent Document 2]
Japanese Patent Kokai Publication No. JP-P2002-43413A
[Patent Document 3]
Japanese Patent Kokai Publication No. JP-P2002-184856A